India's federal detective agency has begun investigating the death of an engineer who complained of corruption in a major road network project.

The Central Bureau of Investigation (CBI) will compile a report into the circumstances leading to the death of Satyendra Dubey, a spokesman said.

Unknown gunmen killed Mr Dubey last month in the eastern state of Bihar.

Prime Minister Atal Behari Vajpayee had asked for a federal probe into the murder, which has shocked India.

Police in Bihar say they have recovered the engineer's mobile phone from the house of a local rickshaw puller.

Dream project

Satyendra Dubey, a 31-year-old civil engineering graduate from the prestigious Indian Institute of Technology (IIT), was working on the country's biggest-ever road project when he died.

About 250,000 people are working on the road project

Under the $12bn scheme, nearly 14,000 kilometres of roads will be built across India.

Mr Dubey was killed nearly a year after he complained to Mr Vajpayee and the road network authorities of what he said was widespread corruption in the project.

In letters to Mr Vajpayee and the network authorities, Mr Dubey alleged that public money was being "looted" from the project.

The Indian Express newspaper, which broke the story on the murder, reported that Mr Dubey had been killed after his name was leaked from the complaint he had sent to the prime minister's office and the road network authority.

His death sparked off unprecedented condemnation and sympathy in a country where there are frequent allegations of public money being siphoned off from large government projects.

Call for new laws

The incident also led political parties to renew demands for laws to protect whistle-blowers.

Nearly 14,000 kilometres of roads will be built

The laws have been pending approval by the federal government for the last two years.

Mr Vajpayee said the people responsible for Mr Dubey's death "wherever they may be, will not be spared".

"Like all right thinking Indians I am shocked and saddened by the murder of Satyendra Dubey, an upright and dedicated officer," Mr Vajpayee said in a statement last week.

The Indian Express newspaper received over 25,000 letters on the incident, websites condemning the death have sprung up, and offers to financially help Mr Dubey's family have poured in.